1. Field of the Invention
The present invention relates to a marine vessel propulsion unit.
2. Description of Related Art
A prior art marine vessel propulsion unit is described in U.S. Pat. No. 6,547,613. The marine vessel propulsion unit includes a propeller shaft, a propeller to be rotated together with the propeller shaft, and a forward-reverse switching mechanism which applies a driving force from an engine to the propeller shaft and rotates the propeller shaft in a forward drive direction or a reverse drive direction. The propeller shaft includes a drive shaft and a driven shaft extending in the front/rear direction.
The drive shaft and the driven shaft are joined by engagement between a plurality of drive teeth provided on the drive shaft and a plurality of driven teeth provided on the driven shaft. The plurality of drive teeth are arranged to be slidable in the front/rear direction along the drive shaft. Also, the plurality of driven teeth are fixed to the driven shaft. The plurality of drive teeth are urged rearward from the front side by a spring member. The plurality of drive teeth are pressed against the plurality of driven teeth by an urging force of the spring member.
The plurality of drive teeth move forward along the drive shaft against the urging force of the spring member while sliding on the plurality of driven teeth when a torque (shock) is applied to the drive shaft by the forward-reverse switching mechanism. In other words, the force (shock) in a rotational direction applied to the drive shaft is converted into a force in the front/rear direction by the plurality of drive teeth and the plurality of driven teeth. Accordingly, the plurality of drive teeth move forward along the drive shaft. Then, the spring member supporting the plurality of drive teeth from the front side is compressed and the shock applied to the propeller shaft is absorbed.